Salmonella

Salmonella

What is Salmonella?

Salmonella is a bacterium which is one of the commonest
causes of food poisoning worldwide. There are over 2,000
different types of salmonella, but with the exception of the
few which cause typhoid or paratyphoid fever, the illness
they cause is similar. Salmonella are widespread in cows,
poultry, pigs, pets and wild animals.

What are the symptoms of Salmonella food
poisoning?

The commonest salmonella infection is due to the presence
of the bacteria in food. After contaminated food has been
eaten the bacteria multiply in the intestines and within 12-36
hours usually cause.

• diarrhoea
• stomach cramps and sometimes
• vomiting and fever.

The symptoms continue for several days and then, in most
people, they cease. Salmonella infection may rarely result in
a very severe illness or even death, particularly in the elderly,
the very young, or someone who is already suffering from
another disease. Even when all the symptoms have
disappeared the bacteria may remain in the gut and thus in
the faeces. When this occurs the people are called carriers
and they pass the infection on to others unless their hygiene
practices are good. The vast majority of people whose
diarrhoea has settled down are not a risk to others and
hence repeated testing of their faeces is not necessary. The
inappropriate use of some antibiotics may encourage and
prolong the carrier state. However, antibiotics may be
beneficial for some patients, such as those with a severe
systemic illness, the elderly and very young, or those with a
damaged immune system.

How do the salmonella bacteria spread?

Food is the commonest source of salmonella for humans.
The food may have been contaminated because the source,
animal or bird, was infected. Salmonella is common among
chickens, studies in 1990 showing that about 50% of frozen
and fresh chicken contain the bacteria. Infections in dairy
herds may lead to contamination of milk, which if not
adequately pasteurised may be consumed directly or used
in the preparation of milk products eg babies' dried milk
feeds and cause infection.

Adequate cooking should eradicate salmonella in food.
However salmonella may be spread in a kitchen from
contaminated to non-contaminated food if hygiene and
catering practices are substandard. Food should be stored
in refrigerators to prevent the bacteria multiplying at room
temperature. Food may also be contaminated by the hands
of infected food handlers if they do not wash them properly
after going to the toilet. If food prepared for a party or
gathering is contaminated an outbreak of salmonella food
poisoning may occur. Individuals nursing or caring for
persons with salmonella diarrhoea may contaminate their
hands with microscopic amounts of faeces which are
carried to their mouths. This is the main reason for
secondary cases within a family or in health-care workers.

How can I prevent getting salmonella infections?

Salmonella infections usually result from a combination of
contaminated foods, poor kitchen hygiene and inadequate
cooking. Attention to good kitchen practices including
thorough cooking of potentially contaminated foods,
especially chicken, should be followed. The Chief Medical
Officer advises against the use of recipes with uncooked or
lightly cooked eggs. However, adequate cooking of eggs,
until the yolk is set, kills salmonellas. Care must also be
taken to ensure that food does not become contaminated
after cooking. Person to person spread is reduced by good
personal hygiene and in particular by thorough hand
washing after going to the toilet or handling clothes soiled
with faeces.

Food poisoning is a notifiable disease and doctors should
inform their local CCDC. Investigations are carried out by
telephone or a visit by Environmental Health officers
enquiring on risk factors and offering advice on hygiene and
the prevention of future infection. For the majority of patients
with a salmonella infection, antibiotic treatment is not
required.

Only those in the following categories need to take advice
from Environmental Health officers or Consultant in
Communicable Disease Control (CCDC):

• Food handlers whose work involves touching unwrapped
food to be consumed raw or without further cooking.

• Health-care, nursery or other staff who have direct contact,
or contact through serving food, with patients very
susceptible to infection or persons in whom a salmonella
infection would have particularly serious consequences.

• Children aged less than five years attending nurseries,
play groups, nursery schools etc.

• Older children or adults who are unable to implement good
standards of personal hygiene eg the mentally ill or
handicapped or the infirm aged.

Salmonella Meningitis

The following information is from the Meningitis Research
Foundation:

Salmonella meningitis is a very rare form of meningitis
caused by salmonella bacteria. From 1975 to 1991, it
accounted for 0.9% of cases of bacterial meningitis in
newborn babies and 0.2% of cases of bacterial meningitis
at other ages*.

Those affected are mostly newborn babies, but cases may
also occur in immunodeficient adults. Babies born
prematurely, with low birth weight, or after prolonged labour
have a higher risk of most forms of neonatal (newborn)
meningitis.

There are many kinds of Salmonella bacteria which often
cause food-poisoning. Infection with Salmonella is very
rarely life-threatening.

In a few rare cases, an unusual form of salmonella
meningitis has been transmitted to babies, pregnant women
and immunodeficient adults by pet reptiles. This is more
widely known in the US where pet reptiles are more popular.
The Chief Medical Officer for England issued advice on this
in February 2000 after the death of a baby from Salmonella
rubislaw meningitis, probably contracted from the family's
pet water dragon. The advice follows:

• Children less than five years old, pregnant women, the
elderly, and people with lowered immunity should avoid
contact with reptiles.

• Babies under one year of age are especially at risk from
direct and indirect contact with reptiles.

• Always wash hands with hot, soapy water after contact with
reptiles, reptile cages, equipment or faeces. Children should
be supervised when handling reptiles to prevent
hand-to-mouth contact.

• Reptiles should be kept away from food and kitchens.
Kitchen sinks should not be used to bathe reptiles, or wash
their cages, dishes or aquariums. Bathtubs should be
cleaned and disinfected with bleach afterwards if they are
used for this.

• If you have a pet reptile, consider keeping it in its cage or
limiting the parts of the house where it is allowed to roam
free.

• Do not eat, drink or smoke while handling reptiles or their
equipment.

(*Neonatal meningitis in England and Wales: a review of
routine national data. Mary B Synnott, Dale L Morse and
Susan M Hall. Archives of Disease in Childhood 1994;
71:f75-f80).